You really don't have any idea what a decorated name is. The users do not change the decorated name. It's a C++ internally generated name to represent operator overloads and to distinguish between overloaded functions. The user must discover what these names are in order to put them into the def file. Also, it's really obvious that you don't understand decorated names because you ignored my other questions.
So far as I'm concerned, whatever the exported name will be, the same exported name will be used when calling the functions, so it should work with just a recompile even if they change the decorated name. Else they would break everything in the language, wouldn't they?